The present invention relates to a reactive energy compensator capable of being electrically connected to an AC electrical network having M phase(s) and having a network frequency, M being greater than or equal to 1, the compensator comprising M phase(s) and including:    at least one input direct voltage bus capable of supplying reactive energy,    at least one voltage inverter connected to the direct voltage bus and capable of converting a direct input current into an alternating output current, the or each inverter comprising two input terminals, M output terminal(s) and M switching branches, each output terminal corresponding to a phase, each switching branch including controllable electronic switches, the or each inverter also comprising a first capacitor having a first voltage at its terminals and a second capacitor having a second voltage at its terminals, the two capacitors being connected serially between the two input terminals of the inverter, and    control means for the electronic switches of the or each inverter, comprising computation means capable of generating a target control current from a current to be compensated, means for combining the target control current and the output current from the inverter to supply a differential current, means for transmitting a control signal capable of driving the switches from the differential current to shape the output current, and correction means, from the first and second voltages, for the control signals of the switches, the correction means being capable of reducing the difference between the value of the first voltage and that of the second voltage.
The invention also relates to a method for balancing half-bus voltages in such a compensator.
Known from the document “Modern active filters and traditional passive filters,” by H. Akagi, published in 2006 in the “Bulletin of the Polish Academy of sciences—Technical sciences—Vol. 4—no. 3,” is a reactive energy compensator including six inverters. The six inverters are connected to each other in parallel, and connected on the one hand to a capacitor bank, and on the other hand to a three-phase network. The six inverters are connected to each other, on the side of the three-phase network, by means of a transformer having six secondaries. The control signals from the electronic switches of those inverters are pulse width modulation signals.
Such a reactive energy compensator placed in an electrical network makes it possible to offset the circulation of reactive power of a load connected on the electrical network that affects the quality of the electricity delivered on the network.
In such an electrical network, certain disruptions, such as disruptions following the connection of an arc furnace on the network for example, can nevertheless cause an imbalance in the values of the first and second voltages of the or each inverter, that imbalance being able to vary from one inverter to the next. The existence of such an imbalance deteriorates the performance of the reactive energy compensator and may lead to the deactivation thereof if the value of the imbalance exceeds a certain threshold.
Known then from document FR 2,947,971 is a conversion device capable of being used in a power supply system for an electrical machine. Such a conversion device includes means for correcting the control signals of the switches of the or each inverter, the means being able to reduce, for the or each inverter, the difference between the value of the first voltage and that of the second voltage. This correction of the control signals is done using specific control algorithms for the switches.
Nevertheless, such a conversion device cannot be used as is in a reactive energy compensator of the aforementioned type to resolve the problem of rebalancing the values of the first and second voltages of the or each inverter. In fact, the transient states due to the electrical disruptions are stronger in a reactive energy compensator than a power supply system, and that solution is not satisfactory in particular in terms of the speed of correction used.